Salazar, who is co-sponsoring the event — scheduled for tomorrow in Denver — supports Whitehouse. The two know each other from having both served as attorney general of their states, Salazar spokesman Cody Wertz said.

But Feinstein, who is up for reelection next year, has not weighed in on the Democratic primary, pitting Whitehouse against Rhode Island Secretary of State Matt Brown (D).

“She has not endorsed in this race,” said Mark Kadesh, Feinstein’s chief of staff. Asked if Feinstein is likely to endorse a primary candidate at a later date, Kadesh said: “Doubtful.”

He said the clearest sign that Whitehouse doesn’t know Feinstein is that the invitation misspells her first name as Diane.

The mistake is particularly odd given that Feinstein was the only member of the Senate Judiciary Committee in 1994 to vote against Whitehouse’s nomination to be U.S. attorney.

Whitehouse was nominated by President Clinton. The Senate subsequently approved him unanimously. Feinstein offered no reason at the time for her no vote.

Jessica Hogle, an associate at Campaign Finance Consultants and the author of the e-mailed invitation, would not discuss the fundraiser or how Feinstein’s name wound up on the invitation. “I don’t recall sending out an e-mail like that,” Hogle said.

Guilfoyle called the Feinstein flap “an honest mistake” made by one of the campaign’s fundraisers.

The Brown campaign declined to comment on the invitation. But a Rhode Island Democrat close to Brown called it “a serious mistake,” saying it raises questions about “the campaign’s credibility.”

The mistake is likely to hit a particularly sensitive nerve at Brown campaign headquarters. Whitehouse, 49, has portrayed himself as the seasoned insider best equipped to beat Sen. Lincoln Chafee (R-R.I.) next year and painted Brown, 35, as an upstart lacking the heft needed to represent Rhode Island on Capitol Hill.

Guilfoyle noted that both congressmen from Rhode Island, Democrats Patrick Kennedy and James Langevin, are serving as national co-chairmen of Whitehouse’s campaign.

Whitehouse’s fundraising operation surged ahead of Brown’s in the second quarter of 2005. Whitehouse raised nearly $783,000 during three-month period from April 1 to June 30, bringing his cash on hand to just over $1 million. Brown, who entered the Senate race months before Whitehouse did, raised a little more than $300,000; his campaign now has $467,000.

A Brown University poll conducted last month showed Chafee leading Whitehouse by five points — 41 percent for the Republican versus 36 percent for the Democrat — while the senator clobbers Brown, 44 percent to 29 percent.

Salazar’s support — and Feinstein’s mistaken listing as a supporter — reinforces Whitehouse’s image as the establishment candidate.

State Reps. Joel Judd and Debbie Benefield, both Colorado Democrats who were also listed as co-sponsors of the Whitehouse fundraiser in Denver, did not return phone calls seeking confirmation of their participation in the event.

Phil Singer, spokesman for the Democratic Senatorial Campaign Committee (DSCC), said yesterday that the committee stays out of Democratic primaries.

Rhode Island is considered one of the Democrats’ best opportunities to pick up a seat next year. As the invitation to the Whitehouse fundraiser puts it: “Democrats need to take back every seat they can in the U.S. Senate, and Sheldon Whitehouse represents our best opportunity to do that in 2006.”

Officials at the National Republican Senatorial Committee (NRSC) have promised they will spend as much as needed to hold onto the seat. Chafee raised close to $406,000 during the second quarter. His campaign has more than $1 million in the bank.

The Whitehouse campaign yesterday issued a new invitation to the Denver fundraiser.

“Please note in my earlier e-mail, I inaccurately stated that Sen. Diane Feinstein is supporting Sheldon,” Hogle wrote, misspelling Feinstein’s first name again. “She is remaining neutral in the race. I apologize for this mistake and any confusion it may have caused.”